mysql indexof function usage instructions

As shown below:

LOCATE(substr,str)

Returns the first occurrence of substring substr in string str. If substr is not in str, returns 0.

mysql> select LOCATE('bar', 'foobarbar'); -> 4 mysql> select LOCATE('xbar', 'foobar'); -> 0

Supplement: LOCATE() method similar to indexOf in MySQL

LOCATE(substr, str), LOCATE(substr, str, pos)

The first syntax returns the position of the first occurrence of substr in string str.

The second syntax returns the position of the first occurrence of the string substr in the string str, starting at position pos. If substr is not in str, the return value is 0.

question:

There are multiple subjects, multiple choice questions under one subject, and four answers (ABCD) for each question. Count the number of ABCD choices for each question in each subject.

SELECT
 sum(
  CASE
  WHEN (LOCATE('A', option name) > 0) THEN
   1
  ELSE
   0
  END
 ) AS A,
 sum(
  CASE
  WHEN (LOCATE('B', option name) > 0) THEN
   1
  ELSE
   0
  END
 ) AS B,
 sum(
  CASE
  WHEN (LOCATE('C', option name) > 0) THEN
   1
  ELSE
   0
  END
 ) AS C,
 sum(
  CASE
  WHEN (LOCATE('D', option name) > 0) THEN
   1
  ELSE
   0
  END
 ) AS D
FROM
 Table name

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